Power of Three (E)
题目
Given an integer n, return true if it is a power of three. Otherwise, return false.
An integer n is a power of three, if there exists an integer x such that n == 3x.
Example 1:
Input: n = 27
Output: true
Example 2:
Input: n = 0
Output: false
Example 3:
Input: n = 9
Output: true
Example 4:
Input: n = 45
Output: false
Constraints:
-2^31 <= n <= 2^31 - 1
Follow up: Could you solve it without loops/recursion?
题意
判断一个整数是不是3的幂。
思路
比较直接的就迭代去除即可。
O(1)方法：在Integer范围内，3的最大幂是3^19=1162261467，且其因数只有3的幂次，那么只要n是1162261467的因数，则n一定是3的幂次。
代码实现
Java
迭代
class Solution {
public boolean isPowerOfThree(int n) {
if (n <= 0) return false;
while (n > 1) {
if (n % 3 != 0) return false;
n /= 3;
}
return true;
}
}
数学计算
class Solution {
public boolean isPowerOfThree(int n) {
return n > 0 && 1162261467 % n == 0;
}
}